Work continued on the boric acid testicular effect. A dose-time study was performed which defined new relationships between endpoints commonly used for testicular assessment. Atrophy was found in the long-term dosed animals. Despite a short biologic half-life and complete clearance from blood in 3-4 days, no testicular recovery was seen. Bone was found to be a long-term depot for boron, but circulating levels were not significantly raised over controls in animals recovering from boron exposure. In vitro studies identified an adverse effect on DNA synthesis in spermatogonia, an effect which was replicated in vivo. A collaborative project will evaluate whether exogenously added paracrine factors will be able to stimulate recovery of spermatogenesis in these atrophic testes. This could ultimately lead to a clinical product that might improve spermatogenesis for sub-fertile males.